The present invention relates to a manufacturing method of a rubber member for tire by overlapping and winding a rubber strip in a circumferential direction and in a spiral shape.
In a pneumatic tire, there are employed various rubber members in which a composition and a cross sectional shape are differentiated in correspondence to a required characteristic of a used portion, for example, a tread rubber, a sidewall rubber, a clinch rubber, a breaker cushion rubber, an inner liner rubber or the like. Conventionally, as the rubber member, there has been used a formed body which is extrusion molded in a desired cross sectional shape of each of the rubber members by a rubber extruder or the like. In a raw tire forming step, each of the rubber members is formed by winding a cut-to-size sheet of the formed body around a forming drum or the like at one circuit.
On the contrary, in recent years, as exemplified in FIG. 10(A), there has been proposed a so-called strip wind method of forming a rubber member c by overlapping and winding a rubber strip a in a circumferential direction and in a spiral shape. As the proposal mentioned above, there are Japanese published patent application 2000-94542, Japanese published patent application 2002-187219, Japanese published patent application 2003-104013 and the like. In this strip wind method, a strip wind body b similar to a cross sectional shape of the rubber member c is formed by winding the rubber strip (a). The drawing illustrates a case that the rubber member (c) is for a side wall rubber. In accordance with this method, since a large-size rubber extruder is not required, and it is not necessary to store the formed body for the rubber member as an intermediate stock, there can be provided with an advantage in addition to a productivity, especially for the tire with a large item rather small scale production, such that a space saving can be achieved and the like.
On the other hand, in the strip wind method, it takes a time for winding the rubber strip. Accordingly, in order to intend to improve productivity, there can be considered to use the rubber strip (a) which has a large cross sectional area and is thick so as to reduce the winding number. However, making the rubber strip thick increases a step (k) in the surface of the strip wind body (wind body), as shown in FIG. 10(B) in an enlarged manner. Further, the increase of the step (k) generates an air remnant between the rubber member (c) and the adjacent other rubber member (c), a vulcanizing metal mold, a bladder or the like. They cause a reduction in uniformity and tire quality. Further, they are left as a scratch on a tire surface, and causes a deterioration in a tire outer appearance. Further, making thick makes it hard to obtain the rubber member having a desired cross sectional shape, thereby deteriorating a forming accuracy of the rubber member and a freedom of a formed shape.